| Summary: | Aquaculture has been a way to produce fish as a protein source for thousands of years and over the past decades aquaculture has been the fastest expanding animal-based food sector in the world. This study focused on quantifying the flows of nitrogen and phosphorus in Atlantic Salmon farming and compared traditional open net farming with a more recent technique, land based recirculating aquaculture system (RAS). The aim was to quantify the difference in emissions of nitrogen and phosphorus between the two types of farming and to quantify the amount of nutrients that could be reused from the respective fish farm. Data were obtained from reports, scientific publications and an application for environmental permit (EIA) for the case Smögenlax Aquaculture AB. The same feed input and salmon output were assumed in the two systems and a substance flow analysis was used to quantify the flows of nutrients. The amount of produced salmon and fish feed/year were taken from Smögenlax Aquacultures EIA. The results showed that a RAS-based Salmon farm emits only 6 % of the nitrogen and 5 % of the phosphorus emitted to the recipient waters in comparison to an open net farm. RAS-based salmon farming also enables the reuse of 19 % more nitrogen and 47 % more phosphorus than an open net farm by using sludge and fish offal from the farm to create biogas and biofertilizers. RAS is still evolving to provide possibilities for large scale salmon farms on land to be both cost and environmental efficient and may in the future be the most common way to farm Atlantic Salmon.
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